Head lice are a worldwide problem. Human head lice (scientific name Pediculus humanus capitis) are tiny parasitic insects that live on the head of a human host, sucking small amounts of blood from the scalp and laying eggs (called NITS) on individual shafts of hair. Head lice are found only on the scalp, and do not live on eyebrow, beard, armpit, or genital hair. Human head lice survive only on people and do not infest pets.
Adult head lice are small, measuring only about 1/16-1/8 inch (1-3 mm) long. They are greyish in color, but turn reddish-brown after they have had a blood meal. Lice have three pairs of legs with elegant, hook-like claws that they can use to hold very tightly to a strand of hair. They are not bothered or removed by shampooing, swimming, brushing, or scratching.
The eggs or nits are tiny (less than 1/16" long) and are shaped like elongated, oval beads. Unhatched eggs are normally pearly white to yellowish white. As the female lays an egg, she glues it to a single strand of hair with a natural cement that rivals super glue in strength. Nits hatch approximately 7-10 days after being laid. Human blood is their only food. In order to survive, young lice must feed shortly after emerging from the egg.
Lice grow in three developmental stages, characterized by three size gradations. They become mature adults sometime between 8 days and 2 weeks after hatching. The time that a louse remains in the egg and as an immature entity varies depending on the individual louse and on temperature and humidity, but in general the time between generations is 15-24 days.
A single female louse lays about 3 eggs per day; occasionally as many as 6 eggs. She can survive for 20-30 days, meaning that she may deposit 60 to well over 100 nits in her lifetime, all on a single human head, or on more than one person if she has an opportunity to travel. This is how lice infestations build so quickly--the life cycle is short and each female louse has a remarkable egg laying capacity.
Head lice bites sometimes cause mild to severe itching due to irritation of the scalp, but in many children they are painless and do not cause the child to scratch. It often takes a while for an infestation to become obvious enough to detect. Detection of lice is usually visual. Unfortunately, lice and their eggs are difficult to see and can be easily missed even by careful parents and school nurses. One must examine the entire scalp and hair for nits (eggs) or lice, a meticulous process that is helped considerably by a magnifying glass, good light, and ample patience.
Lice hide among hairs, so their eggs are usually the first visible sign of a problem. Nits may be confused with dandruff because they are about the same color and size, but dandruff can be easily brushed or blown away. Nits are very securely attached to a strand of hair and are difficult to move or remove even after repeated scraping with a fingernail.
Human head lice are crawling insects; they cannot fly or jump. Lice can travel from one head to another when hair touches, as when children are playing or napping together. Lice may also catch a ride to a different head if they move onto a shared comb or hair brush, or if one crawls onto an article of clothing such as a hat or scarf that is borrowed by another child. Even jackets can transmit lice if one harbors a lurking louse around its collar, and another coat is in contact as they hang close together in a classroom or closet. Lice can also be spread by shared earphones and headsets. Lice must find a new human head within a day or two of leaving their original host so clothing or other articles that have not recently been in circulation among infested children will be safe, assuming that there are no nits on the item. Nits hatch in 7-10 days on or off the host, so detached hair strands with eggs, in a hairbrush for example, remain a risk for transmission to another person, or even back to the brush owner. Hairbrushes should be treated to kill nits. Hats and jackets should be visually inspected for loose hairs with nits.
The length of time that a louse egg or bug can survive away from a person becomes an important issue in understanding how long there is a risk of transmission of lice without direct head contact (on a shared bed or cap, for example). A natural mode of dispersal for a louse is to crawl off of one head, onto a pillow for example, and to hover in that vicinity, hoping that another person will lay his or her head nearby. However, lice will succumb without a source of nutrition. In order to survive, lice need to feed on blood. The scientific data vary somewhat, but studies show that most lice die within 2 days off of a host head, and that all die within 4 days.
Lice eggs (nits) can remain alive off of a person for up to 10 days (on a strand of hair caught in a hair brush, for example). If the juvenile louse hatches and then is brushed onto a head, it can feed and thrive. The combs and brushes used by an infected person are obviously high risk zones for lurking lice. These devices should be treated with for example hot water and/or isopropyl alcohol to reduce the risk of new primary infestations and secondary infestations.
In the United States most doctors and school nurses currently recommend pesticidal shampoos which put noxious chemicals in direct skin contact of treated individuals. Many strains of head lice now appear to be resistant to pesticidal shampoos and even to formulations containing pyrethroids, permethrin, or lindane, which are sometimes prescribed by physicians.
There are a number of "home remedies" that have strong followings among veterans of head lice infestations. There is no scientific data on the efficacy of these approaches, but neighborhood testimonials may persuade one to try one or more. The "oily goop" technique is based on the premise that lice, and their eggs, will die if they can't breathe, and if they are smothered in oil for a sufficiently long period of time, they will die. Choice of preferred oil application is personal: options include such things as petroleum jelly, olive oil, and mayonnaise (regular, not low fat). The entire scalp and all hair must be heavily coated with the oily goop, and it should be massaged in so that lice and their eggs are coated. There is a bit of art involved in this approach because no one is certain of how long the oil should be kept on to ensure suffocation of lice or nits, but the general rule of thumb in common practice is at least about 30 minutes, sometimes overnight.
These sessions are obviously messy. Many people attempt to contain the goop with a shower cap. Grease cutting dish detergents are probably the best recourse in attempting to wash out an oil treatment, but it may take repetitive efforts.
Another widespread approach to lice control is to apply tea tree oil, either straight or in a shampoo. Tea tree oil is available in many stores with natural health products and oils, and the shampoos are often sold in beauty parlors. Some families claim success by using a hair dryer to heat the head and hair, and thereby kill the lice, but lice are hardy critters and this procedure may well hurt the child more than it harms the lice.
In addition to chemical methods for removing lice from human heads, mechanical techniques involving the use of combs are known. However, commonly used combs for this purpose have teeth which are not sufficiently closely spaced (especially at their free ends) to be effective, and the ends are sharp and thus pose a hazard when used on small children. In addition, the free ends of the teeth form a convex edge which reduces the effectiveness of the comb.
Given the fact that chemical methods for removing lice and nits from human (children's) heads expose the infected person to dangerous chemical agents, a need exists for a simple and effective non-chemical method for removing lice and nits from human heads.
Thus, an object of the present invention is to provide such a non-chemical method for removing lice and nits from human heads, such a non-chemical method avoiding the application of pesticides to a human's head.
It is another object of the present invention to provide a comb device which can be used to accomplish the inventive method.
It is another object of the present invention to provide an improved method for detecting lice at an early stage in an infestation and for confirming that lice have not returned to a person who has been previously rid of lice and nits.